Donated whole blood may be separated into its various components and analogous products, thereby making these different blood products available as a transfusion product. For example, a plastic collection bag containing whole blood may be centrifuged to form (1) a supernatant layer of platelet-rich plasma (PRP) and a sediment layer of packed red cells (PRC) with a buffy coat (BC) therebetween or (2) a supernatant layer of platelet-poor plasma (PPP), a sediment layer of PRC, and an intermediate layer such as buffy coat (BC). A bag containing PRP may be centrifuged to form a supernatant layer of plasma and a sediment platelet-containing layer that may be processed to form platelet concentrate (PC). Similarly, a bag containing buffy coat may be centrifuged to form a supernatant layer including platelets and a sediment layer including red cells and the supernatant layer may be separated and processed to form PC.
The separation of whole blood into components as described above may also produce leukocyte contaminated components. It is desirable to reduce the leukocyte concentration of each of the blood components by at least 70%, since the presence of leukocytes may adversely effect the storage life of the components, and/or cause undesirable effects when they are transfused into a patient. Accordingly, blood components may be leukocyte depleted, preferably by passing them through a porous medium such as a leukocyte depletion medium.
Additionally, processing of blood to provide blood components, particularly to provide leukocyte depleted blood products, may lead to the presence of gas or air, in particular oxygen, in the blood components or in the container holding the blood components, e.g., a storage container such as a satellite bag. This may lead to an impairment of the quality of the blood components and may decrease their storage life. Furthermore, the presence of air or gas in the satellite bag may present a risk factor to a patient's being transfused with a blood component.
For this reason, the separation of blood into components has substantial therapeutic and monetary value, placing additional pressure on blood banks to increase component yield and reduce costs per unit of processed biological fluid.
In view of this, there is a growing need for an efficient system and method for separating a biological fluid (e.g., whole blood) into its components. Blood bank personnel have by attempting to increase the yields of blood components in a variety of ways. However, any saving resulting from increasing the yield may be offset by the increased labor cost, if the operator of the processing system must continuously and carefully monitor the system to increase the yield.
However, increasing the yield may be counterproductive. For example, expressing more supernatant PRP from the collection container to increase the yield of platelets in the satellite container may result in the passage of red cells into the satellite container. Since red cells are undesirable, the supernatant fluid must be discarded or recentrifuged so that the red cells may be separated from the platelets.
Accordingly, the previously described methods reflect a generally unsatisfying compromise between the pressing need to maximize the yield of the historically valuable blood components such as PC, plasma, and red cells from whole blood samples, and provide for leukocyte depletion, while minimizing the effort and expense involved.
Because of the high cost and limited availability of blood components, a device comprising a porous medium used to deplete leukocytes from biological fluid should deliver the highest possible proportion of the component present in the donated blood and, at the same time, particularly when used in automated system, decrease or eliminate operator intervention during the processing. An ideal device for the leukocyte depletion of a blood component would be inexpensive, relatively small, and be capable of rapidly processing blood components obtained from about one unit or more of biological fluid (e.g., donated whole blood). Preferably, when the leukocyte depletion device is used in an automated system, the components may be separated and leukocyte depleted in, for example, less than about one hour. Ideally, automatically processing blood while utilizing this device would reduce the leukocyte content to the lowest possible level, while maximizing the yield of a valuable blood component while minimizing an expensive, sophisticated, labor intensive effort by the operator of the system. The yield of the blood component should be maximized while at the same time delivering a viable and physiologically active component--e.g., by minimizing damage due to processing, and/or the presence of air or gas.